Abstract
The volume fraction of strain-induced α' martensite was measured by X-ray diffraction analysis on the fracture surfaces caused by fatigue impact and standard fatigue. The volume fraction of α' martensite increased with increasing ΔK regardless of fatigue impact and standard fatigue. In standard fatigue, this volume fraction increased with increasing stress of ratio and depended on the effective stress intensity range, ΔKeff, at crack tip. If the relation between the volume fraction of α' martensite and ΔKeff in standard fatigue could be used to estimate the effective stress intensity factor, we can get the ΔKeff in fatigue impact. Thus the ΔKeff in fatigue impact was almost equal to maximum stress intensity, Kmax. The fatigue crack growth rate related to the volume fraction of α' martensite, in spite of fatigue impact, standard fatigue and stress ratio. Hence, the plastic zone formed under fatigue impact should be smaller than that from standard fatigue.
